The Immigration Department has confirmed that just over $90 million has been spent operating the temporary immigration detention centres at Manus Island and Nauru.

At a Senate hearing in Canberra on Monday night officials also confirmed that up to December last year, a further $5.2m had been spent transferring asylum seekers to the sites.

Since the Government first announced its plans to re-open the two processing centres – which carry an estimated combined price tag of $2.9 billion - it has been heavily criticised for diverting millions of dollars of aid funding to help pay for the costs of processing asylum claims.

Despite the criticism, Immigration Department officials said they have not ruled out using aid funding to further improve infrastructure and services.

“We would obviously negotiate that at that point in time but we've got to make sure it's relevant to the AUSAID guidelines,” Immigration Department Secretary, Martin Bowles said.

“The potential is there yes, but it just depends on the guidelines and what is the broader use of the facilities and whether it's fully funded, partially funded or however else the guidelines operate.

"It is still part of the government process that we would have to go through to finalise those costs."

Of the $34m already been spent on infrastructure, the majority of work has been carried out at the Nauru centre where the first beds are now being used with the site eventually expected to accommodate 900 asylum seekers. The second centre will likely host a further 600.

Four hundred and fifteen asylum seekers are currently being held on Nauru, with a further 274 in Papua New Guinea.